Generally, a shoe serves simply to protect a wearer's foot from external environments upon his or her activities and further to provide various functions and unique designs for him or her.
The rear axis of the outer sole of the shoe is almost perpendicular to the surface of the ground, so that upon walking, excessive load and pressure are applied to the wearer's foot, thus undesirably making him or her feel easily tired.
Components constituting the foot are basically fixed to each other to perfectly conduct the functions of the foot while the body stands up and walks, and further, they have some orthopedic shapes and structures through their combinations varied in different states.
The forms taken by the foot during walking are varied according to a walking process, and in accordance with the forms taken by the foot during walking, the walking process is largely classified into four steps. For example, as a first step of walking, the heel of the foot comes into contact with the ground, and as a second step of walking, the whole portion of the foot comes into contact with the ground. As a third step of walking, the heel of the foot is raised up from the ground, and as a fourth step of walking, the forefoot of the foot pushes up from the ground. While the four steps are being periodically repeated, the walking is conducted.
First, at the first step of walking wherein the heel of the foot comes into contact with the ground, the foot forms dorsiflexion when the heel of the foot comes into contact with the ground, and at the second step of walking wherein the whole portion of the foot comes into contact with the ground, the ankle of the foot is stretched to form plantar flexion.
Next, at the third step of walking wherein the heel of the foot is raised up from the ground, the ankle is more stretched to develop the plantar flexion, so that joint portions connected between metatarsal heads and proximal phalanges are bent upward. After that, at the fourth step of walking wherein the forefoot of the foot pushes up from the ground, the toes form the plantar flexion, and the metatarsal heads and the phalanges having a given angle through the bending at the third step of walking are stretched, so that the toes push up from the ground. Next, the movement to the first step of walking is ready, and the foot forms the dorsiflexion so that it is separated from the ground. So as to gently conduct the walking at the respective steps, the components of the foot have some orthopedic shapes in their relations, and if the orthopedic shapes are not obtained well due to any problems, the walking becomes inefficient. On the other hand, an excessive pressure or force is applied to the respective portions of the foot, thus making them damaged or disabled. Further, the portions of the foot as required are not sufficiently used, thus making the functions of the foot weakened.
On the other hand, the shoe protects a foot from external heat, cold air, and damages caused by the contact with external objects and releases the impacts applied to the foot while moved. However, the shoe restricts the natural movements of the foot, thus undesirably giving bad influences to the foot.
For example, a conventional shoe outer sole is made of a hard member having a given mechanical strength so as to provide given durability to the shoe itself. In this case, the outer sole does not matter when a wearer stops walking, but when he or she walks or runs, the hard outer sole restricts the natural movements of the foot, so that a larger force than required is used, or a walking form of the foot as required is not obtained well.
Particularly, the raising of the heel of the foot at the third step of walking, that is, the deformation of the foot to take the plantar flexion is not sufficiently conducted. As mentioned above, if the deformation of the foot is not sufficiently conducted at the third step of walking, it is hard that the elasticity of the muscles is accumulated on the foot so as for the toes to push the ground at the fourth step of walking. Thus, the walking efficiency decreases.
Contrarily, if the outer sole is made of too soft material, the durability of the outer sole becomes bad and the stability of the foot becomes weak. Further, separate cost should be needed to obtain given durability according to the materials of the outer sole.
Further, an existing ready-made shoe generally has an outer sole made of an impact-absorbing elastic material so as to reduce grounding impacts during walking or running, but upon grounding, the impact-absorbing elastic material may cause instability to the left and right sides of the foot from the center of the foot according to the positions used. For example, in case of a shoe utilizing the compression of air as a cushion through the formation of an air chamber in the middle of the heel portion thereof, the instability between the left and right sides of the foot becomes severe when the heel of the foot is grounded, thus making the ankle easily damaged.
Many studies have been made to solve the above-mentioned problems. For example, Korean Utility Model Registration No. 2004540430000 (Jun. 3, 2011) discloses a shoe having a sole support, a midsole and an outer sole, wherein the shoe includes an edge formed on the sole support and having one or more bridges located on left and right sides of the forefoot and heel of the foot.
Further, Korean Utility Model Registration No. 2004681440000 (Jul. 19, 2013) discloses a functional shoe including: a midsole having a triple structure made with different hardness; a bridge extended from the top of the midsole to an outer sole and having one or more legs formed integrally with the outer sole; and a net-shaped frame formed on the upper part of the shoe to support the subtalat joint at which pronation starts, wherein the triple structure includes a first low hardness polyurethane layer, a second intermediate hardness polyurethane layer, and a third high hardness polyurethane layer. The triple structure made with the different hardness is increased in hardness it goes from the rear side to the front side. Further, the functional shoe includes a solid portion made of a polymer material to support the medial portion of the foot, and the solid portion is located over the underside and center of the medial side of the shoe.
Further, Korean Patent Application Laid-open No. 1020100042863 (Apr. 27, 2010) discloses a functional shoe that removes the load applied to a foot, while external air is being supplied to the interior of the shoe. In more detail, the load applied to the foot upon walking is released by means of an air bag and a protruding portion to decrease the fatigue of the foot, and further, as the protruding portion and the heel are changed in shape by means of the load applied to the foot, the center of weight of the body moves forward to induce natural walking. Furthermore, the internal air of the shoe is circulated to allow the interior of the shoe to be kept refresh.
Lastly, Korean Patent Application Laid-open No. 1020000036859 (Jul. 5, 2000) discloses a shoe outer sole and a manufacturing method wherein an outer sole made by molding an unvulcanized rubber sheet having prevention sheet made of a sponge sheet or a woven fabric located on top thereof; an edge midsole made by compressing and bonding a foamed and molded E.V.A. material along the top surface edge of the prevention sheet of the outer sole and having a through hole formed on the side surface thereof and a transparent window formed on the through hole in such a manner as to allow the interior of the through hole to be seen; a central midsole located at the center of the edge midsole to maintain lower hardness than the edge midsole and having a cushion member formed on one side of the interior thereof in such a manner as to be compressed and restored from impacts, wherein the medial hardness of the midsole and the lateral hardness of the midsole are different from each other, and the cushion member is adapted to be compressed and restored from the impacts applied to the midsole in such a manner as to be visually checked through the transparent window.